1. Field of the Invention
The present invention relates to detecting and estimating apparatus and method of the optical distortion of transmitting light due to a defect existing on a transparent plate-shaped body, such as a glass plate, or the optical distortion of reflecting light due to the non-uniformity of surface smoothness of a glossy plate-shaped body.
2. Background Art
A defect on a transparent plate, e.g., a glass plate, includes a concave existing on the surface, a fallen foreign material serving as a defect formed by a foreign material fallen on the surface, a concave, like craters, existing at the mark of the fallen foreign material, and a foreign material and bubbles in the glass plate. Further, in the case of a glass plate covered with a transparent film on the surface, a defect of the transparent film includes a pinhole. These defects cause the optical distortion and, then, light is refracted by the optical distortion. Therefore, since the glass plate or the like with the optical distortion becomes a defective product, as an optical substrate, and is not used, it needs to be excluded by inspection.
In a method as disclosed in Japanese Patent Application Publication No. 8-220021, an image of a grid pattern is picked-up by a line sensor camera and the focal point is purposely out of the grid pattern, the difference between a bright portion and a dark portion does not exist to obtain a gray image, the refractive power of a transparent plate-shaped body changes the focal point, and the difference between the bright portion and the dark portion thus exists, thereby detecting a defect. However, in the method, the refractive power of the transparent plate-shaped body is not quantitatively measured on the basis of a unit of lens power (diopter).
On the contrary, in a method as disclosed in PCT Japanese Translation Patent Publication No. 2001-502799, in the case of picking-up an image of a grid pattern by a line sensor camera, the number of CCDs corresponding to the grids is just an integral multiple of the number of grids and the optical distortion is quantitatively detected. However, in order to accurately set the number of CCDs to an integral multiple, the method requires a grid with accurate pitch and width and a lens that does not change the width thereof on the grid pattern corresponding to a pixel at any position at a viewing angle of a telecentric lens.
Further, Japanese Patent Application Publication No. 4-98111 discloses a method for measuring the three-dimensional shape of a surface portion of the living body by fringe scan.